Descriptive statistics for the focal variables and for an illustrative polygenic score (using the p≤ 0.05 threshold) are presented in Table 2. MZ twins’ alcohol problems were correlated at r = 0.53 (232 pairs; p < 0.01), and DZ twins were correlated at r = 0.36 (277 pairs; p < 0.01). This pattern of twin correlations suggests that additive genetic effects accounted for approximately 34% of the variance in alcohol problems. Lower parental knowledge (indexed by higher scores on the parental knowledge scale used here) and higher peer deviance were associated with higher levels of alcohol problems [r(1113) = 0.29 and r(1114) = 0.35, both p-values < 0.01, respectively], which is consistent with previous work indicating that more permissive and deviant environments are associated with a greater amount of adolescent substance use [33,41,42].
